David Mamet's "Homicide" is a brilliant muddle: compelling, exhilarating and, at the same time, profoundly dubious. Certainly there is greatness in it. And just as certainly the moral ice it skates on is precariously thin. It leads us into a forest of dark contradictions, then leaves us stranded, dazzled but bewildered, elated but perplexed.

It's impossible not to feel gravely equivocal about what Mamet has done here. Still, it's Mamet's most complex -- in fact, his best -- film, and one of the most fully articulated expressions of his concerns as an artist. It deals again, as he has in other movies and plays, with a journey of discovery, a descent to the bottom of the self.

The pivotal character is Bobby Gold (Joe Mantegna), a homicide detective whose specialty is hostage negotiation. Among his colleagues he is renowned for his golden tongue; they call him "the Orator." But everyone in Mamet's cop universe has the gift of gab. This is the movie's true glory. "Homicide" is a delirious festival of chatter. No filmmaker working today takes such joy in the sheer pleasure of talk. His characters in this case, mostly inner-city detectives, communicate with each other in a hyperbolic language all their own, in Mamet-speak, a syncopated argot with the precision and improvisational bravura of jazz. They put the American language in the spin cycle and what comes out is a kind of wise-guy, street-corner spritzing, a form of tough-guy poetry that's both eloquent and profane -- poetry with hair on its chest.

But for Mamet's characters, talk isn't simply talk; it's the tie that binds. The detectives working in homicide are Irish, black, Italian, you name it, but they are cops first, a family whose links go beyond race or ethnic background, and for whom language is their badge of brotherhood. It's a hermetic clique, a daisy chain of dedicated professionals, like the real estate salesmen in "Glengarry Glen Ross" and the con men in "House of Games," and nearly everyone outside it is subject to contempt. Belonging is everything.

Bobby's own Jewishness means nothing to him; it's buried under layers of cop. He only thinks about himself as a Jew in the negative. Being Jewish has always meant that he has had something to prove; without really knowing it, it's why he always has to be the first one through the door. Then, an unexpected event forces him to reevaluate his attitudes. On the way to another bust, he becomes accidentally involved in investigating the murder of an old Jewish woman who was killed in the store she had kept for decades in what has now become a black ghetto. It's not a case he wants, but because he is Jewish and the family of the murdered woman has pull downtown, he's ordered to stick with it.

At first, he is outraged. He wants nothing to do with these seemingly paranoid, rich Jews. ("{Blank} them and the taxes they pay," he tells his partner.) Everywhere they look, they see a conspiracy, and he doesn't buy it. Gradually, though, he begins to realize that some of their claims may be true; that, indeed, the murder may have been part of a well-organized antisemitic campaign.

As he digs into the details of the crime, Bobby begins to move away from his society of cops and rediscover his repressed Jewish identity. In searching for what he believes to be his true self, he becomes involved with a militant Jewish group fighting a rabid clan of neo-Nazis who, it's believed, are responsible for the old woman's murder.

This is where Bobby's personal journey -- and Mamet's moral lesson -- begins. It's also where the filmmaker begins to get tangled up in his own thematic shoelaces. Bobby, in pursuing his investigation, must leave behind virtually everything he holds dear, most crucially the allegiance to his society of cops. Spiritually, he undergoes a metamorphosis, and to transform himself he must shift from what is known to what is unknown. The Jews offer to make him one of their own; and though, to his surprise, Bobby wants the same, the price is high, putting his honor and professional ethics as a policeman in conflict with his reawakened Jewish consciousness.

Mamet sets up Bobby's dilemma in either/or terms; there's no way for him to remain true to both groups. He must choose. And in trying to play it down the middle, he loses everything, himself included. Mamet, unfortunately, loses himself too. Or loses us.

"Homicide" is the story of a man who travels to the core of himself and comes up with nothing; it is a scorchingly pessimistic work. It's also lavishly ambitious. But Mamet, in establishing his terms of betrayal for Bobby, overplays his hand. "Homicide" is a thriller, but it also puts forward a definition of evil; and in doing so, the filmmaker carries us into a landscape of symbol and metaphor. As the film progresses, though, Mamet's aesthetic maneuvers become clumsy, and the story's metaphorical skeleton begins to poke through the skin. And though Mamet resolves his metaphors, he does so with a very heavy hand. He bullies them into resolution. Yet, in moral terms, he leaves us without the slightest hope of resolution, with only the flimsiest threads of ambiguity to cling to.

Still, the gravitational pull of Mamet's yarn is difficult to resist. Partly, this is because his actors -- Mantegna, in particular -- express the conflicts within their characters in such viscerally thrilling terms. There's a whole slew of rich character performances here from Vincent Gustaferro, Jack Wallace, Ving Rhames, J.J. Johnston and, especially, as Bobby's partner, W.H. Macyall -- actors whose faces are more familiar than their names. When Bobby's world collapses, we're moved not because of Mamet, but despite him. We're moved, in large part, because Mantegna is such a great actor.

The ambiguities here are resounding, and certain to be controversial, even when Mamet isn't fully in control of them. Mamet has rigorously fashioned a complex modern vision of evil. And though the devil talks a blue streak, he leaves us confounded, shaken, without a compass or the refuge of easy answers.